Apparatus and method for limiting over travel in a probe card assembly

ABSTRACT

Methods and apparatuses for testing semiconductor devices are disclosed. Over travel stops limit over travel of a device to be tested with respect to probes of a probe card assembly. Feedback control techniques are employed to control relative movement of the device and the probe card assembly. A probe card assembly includes flexible base for absorbing excessive over travel of the device to be tested with respect to the probe card assembly.

FIELD OF THE INVENTION

[0001] The present invention relates to testing semiconductor devices.

BACKGROUND OF THE INVENTION

[0002] Individual semiconductor (integrated circuit) devices (dies) aretypically produced by creating several identical devices on asemiconductor wafer using known techniques of photolithography,deposition, diffusion and the like. These processes are intended tocreate a plurality of fully functional integrated circuit devices, afterwhich the individual dies are singulated (severed) from thesemiconductor wafer. In practice, physical defects in the wafer itselfand/or defects in the processing of the wafer often lead to some of thedies being “good” (fully functional) and some of the dies being “bad”(non-fully functional). It is generally desirable to be able to identifywhich of the plurality of dies on the wafer are good dies prior to theirpackaging (encapsulation within a transfer-molded plastic, ceramic ormetal package for subsequent integration into a circuit), and preferablyprior to their being singulated from the wafer. To this end, a wafertester or “prober” is used to make a plurality of discrete pressureconnections to a like plurality of discrete connection pins (or bondpads) on the dies. In this manner, the semiconductor dies can be testedand exercised prior to singulating the dies from the wafer. Aconventional component of a wafer tester is a probe card assembly. Inuse, the wafer or device under test (DUT) and the probe card assemblyare brought together so that the outboard tips of a plurality of probeelements are brought into electrical engagement with corresponding diepads on the wafer.

SUMMARY OF THE INVENTION

[0003] The present invention relates generally to testing semiconductordevices. In one aspect, the invention relates to over travel stops forlimiting over travel of a device to be tested with respect to probes ofa probe card assembly. Other aspects of the invention include feedbackcontrol of relative movement of the device and the probe card assemblyand a probe card assembly with a flexible base for absorbing excessiveover travel of the device with respect to the probe card assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004]FIG. 1 is a side, partially cross-sectional, partiallydiagrammatic view of a semiconductor tester 5 with probe card assembly10 positioned to engage with a semiconductor device 11 (“DUT”) inaccordance with an exemplary embodiment of the present invention.

[0005]FIG. 2 is a side, partially cross-sectional view of the probe cardassembly 10 of FIG. 1 shown in engagement with DUT 11.

[0006]FIGS. 3a-3 f are side, cross-sectional views showing, in stages,the fabrication of probe tips 21 and stop plates 23.

[0007]FIGS. 4a-4 c are side, partially cross-sectional views showing, instages, fabrication and assembly of space transformer assembly 40.

[0008]FIG. 5 is a bottom view of the probe card assembly 10 of FIG. 1.

[0009]FIG. 6 is a side, partially cross-sectional view of a probe cardassembly 45 positioned to engage with a semiconductor device 11 (“DUT”)in accordance with an alternative embodiment of the present invention.

[0010]FIG. 7 is a side, partially cross-sectional view of the probe cardassembly 45 of FIG. 6 shown in engagement with DUT 11.

[0011]FIG. 8 is a side, cross-sectional and partially diagrammatic viewof a probe card assembly 56 in accordance with another embodiment of thepresent invention.

[0012]FIG. 9 is a plan, diagrammatic view of the probe card assembly 56of FIG. 8.

[0013]FIG. 10 is a side, cross-sectional view of a portion of probe cardassembly 56 of FIG. 8 and positioned to engage with a wafer 71.

[0014]FIG. 11 is a side, cross-sectional view of the probe card assembly56 of FIG. 10 and shown in engagement with wafer 71.

[0015]FIG. 12 illustrates an exemplary microprocessor based controller.

[0016]FIGS. 13 and 14 illustrate exemplary processes for controllingmovement of a wafer into contact with a probe assembly.

[0017]FIGS. 15a-15 c illustrate a probe card assembly with a flexiblebase.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0018] For the purposes of promoting an understanding of the principlesof the invention, reference will now be made to the embodimentsillustrated in the drawings and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended, and any alterationsor modifications in the illustrated device, and any further applicationsof the principles of the invention as illustrated therein arecontemplated as would normally occur to one skilled in the art to whichthe invention relates.

[0019] Referring to FIG. 1, there is shown a semiconductor tester 5 fortesting semiconductor devices. Tester 5 generally includes a probe cardassembly 10, support structure 12, control apparatus 13 and asemiconductor device holder 18. Probe card assembly 10 is shownpositioned to engage with and test a semiconductor device 11 (otherwiseknown as a device under test or “DUT”) in accordance with the presentinvention.

[0020] The exemplary probe card assembly 10 illustrated in FIG. 1generally includes a base assembly 14, a space transformer 15, aplurality of probes 16 (eight of many shown), and a plurality ofovertravel stop assemblies 17. Support structure 12 supports probe cardassembly 10 and can be operable to move probe card assembly 10 towardDUT 11 or to hold probe card assembly 10 stationary while DUT 11 ismoved toward probe card assembly 10. Holder 18 is connected with supportstructure 12 and is configured to hold DUT 11 stationary during thetesting procedure while probe card assembly 10 is moved toward DUT 11 orto move DUT 11 toward probe card assembly 10. Semiconductor deviceholder 18 can be in any configuration that securely holds semiconductordevice 11 during testing. Holder 18 may also be configured to grasp asemiconductor device 11 from an indexing unit, move it into testingposition, hold it and/or move it during testing, and then move it out oftester 5 to an output station. Holder 18 is contemplated in oneembodiment to include electronic connection apparatus for electronicallyconnecting or facilitating such connection of semiconductor device 11with control apparatus 13. Control apparatus 13 is connected withsupport structure 12 and DUT holder 18 and includes elements such ascomputer hardware and software for controlling movement of probe cardassembly 10 and/or DUT 11. In alternative embodiments, control apparatus13 does not rely on computer components to control movement of probecard assembly 10 and/or DUT 11, but instead provides any type of manualactuation apparatus including, but not limited to levers, linkages, arack and pinion mechanism, cables, pulleys and/or similar devices formoving probe card assembly 10 and/or DUT 11. Control apparatus 13 isalso electronically connected with probe card assembly 10 andconnectable to DUT 11 (either individually or through holder 18) to sendand receive data testing signals thereto and therefrom.

[0021] Although probe card assembly 10 is illustrated in FIG. 1 ascomprising a base 14 and a space transformer 15, probe card assembly maybe any type of probe card assembly. For example, probe card assembly 10may be as simple as only a base 14 to which probes 16 and over travelstops 17 are directly attached. As another example, probe card assembly10 may comprise a more complex assembly of parts, such as the probe cardassembly illustrated in U.S. Pat. No. 5,974,662, which is incorporatedby reference herein in its entirety. Probes 16 may be any type ofprobes, including without limitation needle probes, buckling beam probes(e.g., “COBRA” probes), bumps, posts, and spring probes. Nonexclusiveexamples of spring probes include the spring contacts described in U.S.Patent Application Publication 2002/0055282 A1, U.S. patent applicationSer. No. 09/032,473 (filed Feb. 26, 1998), U.S. patent application Ser.No. 10/262,712 (filed Jul. 24, 2002), U.S. Pat. No. 6,268,015, and U.S.Pat. No. 5,917,707, all of which are incorporated by reference in theirentirety herein.

[0022] DUT 11 is a semiconductor wafer on which have been fabricated aplurality of integrated circuit chips or “dice” (not shown). Eachindividual die has a number of pins or bond pads 19 for providing power,ground, and signals such as data, address, control, etc. to the die. DUT11 may contain many hundreds of bond pads 19 disposed in close proximityto one another (e.g. 5 mils center-to-center), and the bond pads may bearranged in configurations other than a single row near the edge of thedie. Because of the close proximity of many bond pad arrays, the tips ofprobes 16 may often need to be spaced more closely to one another(relatively fine pitch) than the connections to their base assembly 14.“Space transforming” (sometimes referred to as “pitch spreading”) maytherefore be incorporated in the present application by a spacetransformer, representatively shown at 15 (comparable to element 506 inthe U.S. Pat. No. 5,974,662).

[0023] Space transformer 15 facilitates making a reliable testingconnection between the plurality of probes 16 and the corresponding bondpads 19 of DUT 11 by redirecting spatially indiscriminate inputconnections (not shown) from base assembly 14 to a specificallyorganized array of probes 16 that align with the mating array of bondpads 19 as shown, for example, in FIG. 1. The input connections (notshown) from base assembly 14 to space transformer 15 may be formed inany suitable manner.

[0024] Each of the exemplary plurality of probes 16 includes a resilientinterconnecting wire element 20 and a probe tip 21. Each exemplary overtravel stop assembly 17 includes a pair of substantially rigid posts 22and a stop plates 23. Each post 22 is rigidly mounted in any suitablemanner at one end to space transformer 15, and at its opposing end ismounted to a stop plate 23. As DUT 11 and probe card assembly 10 arebrought together and probe tips 21 engage with corresponding bond pads19, the resilient, spring-like wire elements 20 deform (as shown in FIG.2). The neighboring over travel stop assemblies 17 engage DUT 11 at apredetermined distance (a proximity limit) to physically limit how closeDUT 11 and probe card assembly 10 can get, and consequently to ensurethe proper pressure engagement between probe tips 21 and bond pads 19.

[0025] Referring to FIGS. 3a-3 g and 4 a-4 c, there is shown anexemplary method for making a portion of probe card assembly 10 inaccordance with one embodiment of the present invention. As shown inFIG. 3a, a plurality of pits 26 are etched in a sacrificial substrate27, such as a semiconductor wafer, using known methods such as masking.The number and arrangement of pits 26 correspond to the number andarrangement of bond pads on the corresponding DUT to be tested. Thesepits 26 will form the ends 28 of probe tips 21. Referring to FIG. 3b, anoptional first mask layer (mask 31) is formed, using known methods, oversacrificial substrate 27, proximal to pits 26, and in a specific sizeand shape. Mask 31 is preferably a photoresist material, such as SU8.

[0026] Referring to FIG. 3c, a release (and/or seed) material 32 isformed over the substrate and mask 31. Release material 32 is applied tofacilitate separation between sacrificial substrate 27 and mask 31thereunder and the probe tips 21 and stop plates 23 formed on topthereof. Also, if the probe tips 21 and stop plates 23 are formed byelectroplating, release material 32 will provide the conductive layernecessary for electroplating. In one embodiment, release material 32comprises aluminum. Other appropriate materials may be used for releasematerial 32 including, but without limitation, copper, titanium,tungsten or alloys of these and/or other materials including materialsmade of two or more layers of such materials that function as describedabove. For purposes of illustration, the dimensions of certain elementsshown in the figures may be exaggerated or not in proportion.

[0027] Referring to FIG. 3d, a second mask layer (mask 33) is formed ina specific pattern over sacrificial substrate 27, mask 31 and releasematerial 32, as shown. Mask 33 defines a plurality of cavities 35 and 36that are sized and shaped to create probe tips 21 and stop plates 23,respectively. A preferably conductive material is then deposited intocavities 35 and 36 to form probe tips 21 and stop plates 23, as shown inFIG. 3e. The material used to form tips 21 and plates 23 is generallydesired to be conductive, non-oxidizing, and chemically non-reactive.Examples of appropriate materials include, without limitation,palladium, gold, rhodium, nickel, cobalt, silver, platinum, conductivenitrides, conductive carbides, tungsten, titanium, molybdenum, rhenium,indium, osmium, rhodium, copper, refractory metals, and their alloys aswell as alloys of these and/or other materials. Any appropriate methodmay be used to deposit such material into cavities 35 and 36 such as,but without limitation, chemical vapor deposition, physical vapordeposition, sputtering, electroless plating, electron beam deposition,and thermal evaporation. Alternatively, a non-conductive material may beused for either or both of probe tips 21 and stop plates 23 such asaluminum oxide, aluminum nitride, etc. In the event a non-conductivematerial is used for probe tips 21, at least the ends 28 of tips 21 mustbe made conductive and must be electrically connected to wire elements20. This may be done in any suitable manner such as, and withoutlimitation, by coating the exterior surface of probe tips 21 with aconductive material. After formation of probe tips 21 and stop plates23, mask 33 is removed to expose the probe tips 21 and stop plate 23, asshown in FIG. 3f. Because the tips 21 and stop plates 23 are formedlithographically, they may be formed with relatively precise spatialrelationships to each other.

[0028] Referring to FIG. 4c, the assembly 36 of probe tips 21 and stopplates 23 of FIG. 3f are shown having been connected to spacetransformer 15. More specifically, interconnecting wire elements 20connect probe tips 21 to space transformer 15 to form the plurality ofprobes 16, and stop plates 23 are connected to and a fixed distance fromspace transformer 15 by posts 22 to form over travel stop assemblies 17.In one embodiment, such wire elements are formed and connected to spacetransformer 15 using the wire bond technique wherein each wire is madeof a relatively soft, malleable material and is bonded in a knownmanner, at the desired location, to space transformer 15 (FIG. 4a).Posts 22 may be formed in like manner, but may be thicker to be rigidand/or made of a material that is more rigid. The wire may then beovercoated with a harder, resilient material. Exemplary descriptions ofthis technique are provided in U.S. Pat. Nos. 5,476,211, 5,917,707, and6,336,269, which are hereby incorporated by reference.

[0029] Alternatively, elements 20 need not be wires. For example,elements 20 may be resilient spring-like structures formedlithographically by applying and patterning a masking layer to spacetransformer 15 and then depositing material in the openings in themasking layer or layers as generally illustrated in FIGS. 3b and 3 eabove. Indeed, elements 20 may be fashioned in a variety of shapes bymolding the masking layer(s) to have the negative of the desired shape(an example of this technique is as described in U.S. Patent ApplicationPublication 2002/0055282 A1, which is incorporated in its entiretyherein by reference) or by using multiple masking layers with differentpatterned openings to define the negative of the desired shape ofelements 20 (an examples of this technique are described in U.S. patentapplication Ser. No. 09/032,473 (filed Feb. 26, 1998) and U.S. Pat. No.6,268,015, both of which are also incorporated in their entirety hereinby reference). Alternatively, such lithographic techniques may be usedto build elements 20 over the tips 21 and posts 22 over stop plates 23following the step illustrated in FIG. 3e. All of the foregoingtechniques may also be used to make posts 22.

[0030] As should be apparent from the foregoing, the invention is notlimited to any particular type of probe. Rather, the present inventioncontemplates use of any appropriate probe including, without limitation,needle probes, buckling beam probes (e.g., “COBRA” probes), bumps,posts, and spring probes, examples of which are discussed above.Moreover, the probes may be made and assembled into an array in anymanner. For example, probes may be made lithographically, by machining,by stamping, by molding, by microelectrical mechanical system (MEMS)processes, etc. and then assembled into an array. An example in whichprobes are made using a MEMS process and then assembled into an array isdiscussed in U.S. patent application Ser. No. 10/262,712 (filed Jul. 24,2002), which is incorporated in its entirety herein by reference.

[0031] The stop structures may also be made and assembled in of theforegoing ways. Typically, posts 22 are made with sufficient rigiditythat, upon engagement of over travel stop assemblies 17 with DUT 11,posts 22 will not significantly deform and will physically stop furthertravel of DUT II toward probe card assembly 10.

[0032] Referring again to the example illustrated in FIGS. 3a-4 b, asshown in FIG. 4b, the assembly 38 (FIG. 4a) of wire elements 20 andposts 22 extending from space transformer 15 is then brought togetherwith the assembly 36 (FIG. 3f) of probe tips 21 and stop plates 23formed upon on sacrificial substrate 27. As shown, probe tips 21 andstop plates 23 are all sized and located on sacrificial substrate 27,and wire elements 20 and posts 22 are all sized and located on spacetransformer 15, so that each probe tip 21 aligns with a correspondingwire element 20 and each stop plate 23 aligns with a corresponding pairof posts 22. Probe tips 21 are then permanently bonded to wire elements20, and stop plates 23 are permanently bonded to posts 22. Such bondingmay be performed in any appropriate manner such as, and withoutlimitation, soldering or brazing. Such connection methods are describedwith reference to FIGS. 8D and 8E in the U.S. Pat. No. 5,974,662.

[0033] Following connection of the probe tips 21 and stop plates 23 towire elements 20 and posts 22, respectively, sacrificial substrate 27 isremoved by any appropriate method such as, but without limitation,etching or dissolving. The resulting space transformer assembly 40 maybe joined with other components to form a probe card assembly 10, suchas the probe card assembly shown in FIG. 5 of the U.S. Pat. No.5,974,662.

[0034] In use, when DUT 11 and probe card assembly 10 are broughttogether and probe tips 21 engage with corresponding bond pads 19, theresilient, spring-like wire elements compress or deform (as shown inFIG. 2). To ensure that DUT 11 moves close enough to probe card assembly10 to allow all of probes 16 to deform and achieve a sufficientlyresistive spring force and thus reliable pressure contact with theircorresponding bond pads 19, neighboring over travel stop assemblies 17engage DUT 11 at a predetermined distance of travel to physicallypreclude additional over travel. With probe card assembly 10 constructedas described and shown in FIG. 1, the combined depth of pits 26 and thethickness of mask 31 corresponds to the over travel distance 41 (FIG. 1)permitted by the present invention.

[0035] The probe card assembly 10 of FIG. 1 shows just eight probes 16and a pair of neighboring stop assemblies 17. Another configuration isshown in FIG. 5 where the probe card assembly 42 (bottom view) has twoarrays 43 and 44, each containing 48 probes 16 extending downwardly fromspace transformer 15, and where there are six over travel stopassemblies 17 spaced around the outside of the two arrays 43 and 44. Itis contemplated that probe card assembly 42 or a similar probe cardassembly may be used to test DUT's with fewer bond pads 19 than arecontained in the corresponding array(s) of probes 16. Such excess probes16 that do not contact a corresponding bond pad (or an inactive bondpad) can be deselected by software.

[0036] The test system in which the probe card assembly of the presentinvention is incorporated may operate to move DUT 11 toward a stationaryprobe card assembly 10 or to move probe card assembly 10 toward astationary DUT 11 or to move both DUT 11 and probe card assembly 10towards each other. Further, such test system may be configured for suchmovement by the DUT 11 and/or probe card assembly 10 to be effectedmanually or automatically. It is contemplated that such test system willincorporate any appropriate configuration of machinery, computerhardware and software to effect such manual or automatic movement, toprovide for adjustment of the limits, path and rate of such movement,and to receive, process and display output data produced during suchmovement and from the engagement between the DUT and the probe cardassembly.

[0037] Alternative embodiments are contemplated wherein there are moreor less than two posts 22 connecting and holding each stop plate 23.Alternative embodiments are contemplated wherein plates 23 are in shapesother than the relatively planar and rectangular configuration shown.Alternative embodiments are contemplated wherein posts 22 are not rigid,but instead are somewhat resilient to provide a degree of “give” or“compliance” when DUT 11 engages with over travel stop assemblies 17.For example, as shown in FIG. 6, a probe card assembly 45 is shown inaccordance with another embodiment of the present invention wherein thestop plates 46 and 47 of over travel stop assemblies 48 and 49 are heldby resilient posts 50. (Like probe card assembly 10 of FIG. 1, the probecard assembly 45 shows just eight probes 16 and just two over travelstop assemblies 48 and 49. The invention contemplates any number ofprobes and stop assemblies to properly engage with the bond pads of aDUT 11 to be tested). Posts 50 may be formed and connected to spacetransformer 15 using any appropriate method, including those techniquesdiscussed herein for forming and connecting wire elements 20.

[0038] One benefit of making posts 50 resilient is realized in the eventthat DUT 11 is at all non-planar, that any of stop plates 46 and 47 areor have become non-planar, that stop plates 46 and 47 of over travelstop assemblies 48 and 49 are or have become mutually non-planar, and/orthat DUT 11 is not parallel to the plane of the stop plates 46 and 47 atthe moment of engagement therewith. Thus, referring to FIG. 7 where, inexaggerated fashion, DUT 11 is shown to be non-planar at the moment ofinitial engagement, the resiliency of posts 50 allows the first stopplate 46 to engage, and its resilient posts will deform until the otherstop plate 47 likewise engages. The resiliency of posts 50 is selectedto permit such deformation by one or a few of the posts when necessary,but to also still provide a physical over travel limit when all the overtravel stop assemblies 48 are engaged. Alternative embodiments arecontemplated where posts 50 are made to be both rigid and resilient.That is, a portion of each post 50 is made resilient to enable a limiteddegree of give (as shown in FIG. 7) and another portion of each post ismade rigid to define the maximum limit of give, and thus overtravel.Alternative embodiments are also contemplated wherein plates 23 are notrigid, but instead are somewhat resilient to provide a degree of “give”or “compliance” when DUT II engages with over travel stop assemblies 17.

[0039] Alternative embodiments are contemplated wherein one or more overtravel stop assemblies are wired to provide a signal that thecorresponding DUT 11 has been engaged. Such signal may simply indicateengagement or may signal the extent of engagement (e.g., by signaling adegree of force exerted by the wafer on the probes or the over travelstop). For example, such signal may provide a binary output x: nocontact (x=0), contact (x=1). Alternatively, a more detailed responsemay be provided by the output value x: no contact (x=0), contact (0<x<1)where any x greater than 0 indicates contact and the value of x greaterthan 0 and less than or equal to 1 indicates the extent of travel of theDUT from initial contact up to and including the limit of travel. Suchoutput signal is contemplated to be received as input by computercomponents connected with the probe card assembly and displayed in anyappropriate form and/or used to further control the overall probetesting operation. Typically, such output signal would be sent to thetester or prober, which would then stop movement of the probe cardassembly toward the semiconductor wafer when the desired over travellimit is reached.

[0040] An example of such assembly in shown in FIG. 8, where a probecard assembly 56 includes over travel stop assemblies 57 that are wiredto provide over travel position output signals. Like probe card assembly45 of FIG. 6 and similar to the probe card assembly 500 of FIG. 5 of theU.S. Pat. No. 5,974,662, probe card assembly 56 includes an array 58 ofprobes 59 and over travel stop assemblies 57 mounted to a spacedtransformer 61, which is electronically connected by variousinterconnection wire elements 62 and an interposer 63 to a probe cardassembly 65. An over travel control unit 66 is wired to the over travelstop assemblies 57 whereby the over travel output signals aretransmitted to control unit 66, which transmits corresponding signals tothe tester/prober (not shown). The allowable over travel is indicated at67. FIG. 9 is a plan view of the probe card assembly 56 showingdiagrammatically one exemplary placement of over travel stop assemblies57 relative to the array 58 of probes 59.

[0041]FIGS. 10 and 11 illustrate one exemplary arrangement for detectingcompletion of a desired amount of over travel of bond pads or pins 73,74 of wafer 71 with respect to probes 59. Referring to FIG. 10, the overtravel stop assemblies 57 are arranged in adjacent pairs. Thus, at eachof the four sites of the probe card assembly 56 of this embodiment (FIG.9), probe card assembly 56 includes a pair of over travel stopassemblies 69 and 70. In each die on the wafer 71 to be tested, the bondpads or pins 73, 74 comprise functioning pins 73 and dummy pins 74.(Pins 73, 74 in FIGS. 10 and 11 are shown as having slightly differentheights due to inherent manufacturing imprecision.) Functioning pins 73are functional in providing the desired power, ground and signalcapabilities for their corresponding die 76 (or 77), while dummy pins 72are shorted to ground.

[0042] In use, when wafer 71 and probe card assembly 56 are broughttogether, probe tips 59 will engage with corresponding pins on the DUT11 (device under test) 78. Because of the resiliency of the wire element80 of each probe 59, each probe 59 will deform as necessary and engagewith each of its corresponding pins 73 and 74. It should be noted thatthere may or may not be a probe 59 that corresponds to a particulardummy pin 74. It should also be noted that the contact plates of overtravel assemblies 69 and 70 are preferably made to correspond to knownlocations of dummy pins 74 on wafer 71. A circuit will be completed anda corresponding signal will be generated and transmitted through controlunit 66 to the prober/tester (not shown), and movement of probe cardassembly 56 toward wafer 71 will stop. The invention contemplates thatthe system software will be configured to control the testing operationin response to any desired contact combination. That is, in oneembodiment, contact by any two adjacent over travel stop assemblies(i.e. 69 and 70) with dummy pins will cause movement of probe cardassembly 56 to stop. Alternatively, referring to FIGS. 8 and 9, any oneover travel stop assembly (i.e. 69) at one side 81 of array 58 and anyone over travel stop assembly (i.e. 82) at another side 83 (or 84 or85), can be programmed to stop movement of probe card assembly 56.Alternatively, just one over travel stop assembly (i.e. 69) could beprogrammed to stop movement of probe card assembly 56.

[0043] Alternative embodiments are contemplated wherein two or more overtravel stop assemblies are wired as above and the output thus indicateswhich over travel stop assemblies have engaged with the DUT 11 and byhow much. Such output, from just one or from a plurality of the overtravel stop assemblies, is contemplated to be made available for displayor other recognition by a human or machine. Thus, such output may simplybe indicated by a single LED flashing or by a buzzer. Alternatively orin addition, a display screen may diagrammatically indicate the entireprobe card assembly layout and show by any appropriate display whichover travel stop assemblies have been engaged and by how much.Alternatively or in addition, the output signal may be received by acomputer or other machine and acted upon. For example, a signal that anover travel stop assembly has engaged a bond pad or pin may cause thesystem to cease movement of the probe card assembly toward the DUT 11,or visa versa, or movement for only another pre-programmed distance.Where the output signal indicates the extent of engagement, suchinformation can be used by the human user or the machine to adjust thelimits of movement of the DUT relative to the probe card assembly, aswell as the rate of such movement.

[0044]FIGS. 13 and 14 illustrate exemplary methods for automaticallycontrolling movement of a wafer to be tested into contact with a probecard assembly, and FIG. 12 illustrates a feedback controller 530 thatmay implement any of the processes of FIGS. 13 and 14. The exemplaryfeedback controller 530 illustrated in FIG. 12 is a microprocessor basedcontroller and may be, for example, part of control apparatus 13. Asshown, it includes a digital memory 532, a microprocessor 534, and aninput/output port 536. Input data 538 is received and output data 540 isoutput through input/output port 536. The digital memory 532 may be anytype of memory including an electronic memory, an optical memory, amagnetic memory, or some combination of the foregoing. As just twoexamples, digital memory 532 may be a read only memory, or digitalmemory 532 may be a combination of a magnetic or optical disk and arandom access memory. Microprocessor 534 executes instructions (whichmay be in the form of software or microcode) stored in digital memory532.

[0045] The exemplary methods illustrated in FIGS. 13 and 14, which maybe implemented in software and executed on a microprocessor based systemsuch as the one illustrated in FIG. 12, will be explained with referenceto a probe card assembly 56 such as the one illustrated in FIGS. 8-11 ina tester 5 like the one illustrated in FIG. 1. For purposes ofdiscussion only, it is assumed that a wafer such as exemplary wafer 71is moved while probe card assembly 56 is held stationary. Of course, thewafer could alternatively be held stationary and probe card assemblymoved, or both the wafer and the probe card assembly could be moved. Thewafer 71 may be supported by any appropriate means, such as the waferholder 18 illustrated in FIG. 1, which itself is moved by anyappropriate means, such as an electric motor (not shown). Output data540 (FIG. 12) includes signals that control movement of the wafer 71(e.g., by moving the wafer holder 18), and input data 538 includessignals from over travel control unit 66 or other sensors (e.g., theoutput of over travel control unit 66 may be directed to feedbackcontroller 530 as input data 538).

[0046] The exemplary method illustrated in FIG. 13 utilizes one or moresensors for detecting when the wafer 71 has been moved into contact withthe probes 71 and then further moved by a desired amount of over travelpast first contact. For illustration purposes, the sensor(s) is assumedto comprise over travel stop assemblies 69, 70 wired to detect contactas illustrated in FIGS. 10 and 11. It should be understood, however,that any sensor for detecting or estimating when the wafer 71 has beenmoved the desired over travel distance may be used. Such sensors includeby way of example acoustic sensors, optical sensors, etc., which may beused to detect, for example, when the over travel stops reach aparticular position. It should also be noted that one to several suchsensors may be used, and if a plurality of sensors are used, the sensorsmay be arranged in any pattern on probe card assembly 56. The pattern offour sensors 81, 83, 84, 85 illustrated in FIG. 9 is but one exemplarypattern.

[0047] Turning now to the exemplary method illustrated in FIG. 13, thisexemplary method begins after wafer (e.g., wafer 71 shown in FIGS. 10and 11) has been placed on a moveable holder (e.g., wafer holder 18illustrated in FIG. 1), and pads or pins 73, 74 of wafer have beenaligned with probes 59, as illustrated in FIG. 10. As shown in FIG. 13,the first step 110 is to move the wafer 71 toward the probe cardassembly 56. At step 112, it is determined whether the pins 73, 74 onwafer 71 have been moved into contact with probes 59 and over traveledthe desired distance. If no, movement of the wafer 71 toward the probecard assembly 56 continues (step 110). If yes, movement of the wafer 71is stopped at step 114.

[0048] Determining whether pins 73, 74 have reached the desiredover-travel (step 112) may be detected or estimated in any way. As justone example, stop structures 69, 70, such as those illustrated in FIGS.10 and 11 may be configured so that an over travel sensor 66 generates asignal when over travel stops 69, 70 contact pins 73, 74. That signalmay be input to controller 530 as input signal 538. As mentioned above,other types of sensors may be used. Also, any number of sensors may beused, and if multiple sensors are used, they may be positioned in anysuitable pattern. If multiple sensors are used, a signal indicating thatthe desired amount of over travel has been reached may be triggered byany one or more of the sensors in any desired pairing or sequence. Forexample, referring to the exemplary pattern of sensors 81, 83, 84, 85shown in FIG. 9, a over-travel-reached state may be found to beaffirmative at step 112 when any one of the sensors 81, 83, 84, 85 isactivated. As another nonexclusive example, the over-travel-reachedstate may be found to be affirmative at step 112 only after all foursensors 81, 83, 84, 85 are activated. As another example, theover-travel-reached state may be found at step 112 after a pair ofsensors (e.g., opposite pairs 81, 83, or pairs 84, 85) are activated.Many other combinations are possible.

[0049] Turning now to the exemplary method illustrated in FIG. 14, thisexemplary method also begins after a wafer (e.g., wafer 71 shown inFIGS. 10 and 11) has been placed on a moveable holder (e.g., waferholder 18 illustrated in FIG. 1), and pads or pins 73, 74 of wafer 71have been aligned with probes 59, as illustrated in FIG. 10. As shown inFIG. 14, the first step 202 is to move the wafer 71 toward the probecard assembly 56 at an initial speed. During this movement, the forcethe wafer pads or pins 73, 74 exert against probes 59 is determined atstep 204, and it is determined at step 206 whether the force exceeds apredetermined maximum force. (Of course, before first contact betweenthe pads or pins 73, 74 and probes 59, the force is zero.) If yes,movement of the wafer 71 toward the probe card assembly 56 is stopped atstep 210 (e.g., controller 530 issues control signals 540 that causemovement to stop). If, however, the determined force is less than themaximum force (step 206), at step 206, the speed of the movement of thewafer 71 toward the probe card assembly 56 is adjusted in accordancewith the force determined at step 204 (e.g., again the controller 530issues control signal(s) 540 that adjusts the speed). Preferably, thespeed is decreased as the force increases. The steps of moving the wafer71 toward the probe card assembly 56 (step 202), determining the force204, and adjusting the speed of the wafer 71 (step 208) are repeateduntil the force on the probes 56 exceeds the maximum force (step 206).It should be noted that step 208 is optional. That is, the process ofFIG. 15 can be performed without adjusting the speed following anegative determination at step 206.

[0050] Again, there are many different types of sensors that may be usedto determine or estimate the force on a probe. For example, over travelstops 69, 70 may be fitted with force measuring sensors (e.g., apiezoelectric material). Alternatively, force measuring device(s) may beconnected directly to one or more probes 59. Also, one or more suchsensors may be used. If more than one is used, the step of determiningthe force 204 may comprise averaging the forces detected by all of thesensors.

[0051]FIGS. 15a-15 c illustrate a probe card assembly 446 in which base414 is made of a flexible material. As will be seen, because the base414 is flexible, it absorbs extra over travel. As shown in FIG. 15a,wafer holder 18 brings wafer 11 into first contact with probes 16. Asshown in FIG. 15b, wafer holder 18 moves wafer 11 past the point offirst contact by an over travel distance 41. As shown in FIG. 15c, forwhatever reason, wafer holder 18 moves wafer 11 beyond the desired overtravel 41 by an additional over travel distance 441. Normally, theadditional over travel 441 could cause excessive forces to be exerted onthe over travel assemblies 17 and possibly the probes 16. As also shownin FIG. 16c, however, the base flexes, absorbing all or at least part ofthe additional over travel 441, eliminating or at least reducing theexcessive forces caused by the additional over travel 441. The base 414may be made of any material that is sufficiently rigid to support probes16 but sufficiently flexible to absorb all or part of over travel 441.Examples of such materials include, without limitation, printed circuitboard material, Mylar, organic materials, rubbers, and plastics.

[0052] While the invention has been illustrated and described in detailin the drawings and foregoing description, the same is to be consideredas illustrated and not restrictive in character, it being understoodthat only the preferred embodiment has been shown and described and thatall changes and modifications that come within the spirit of theinvention are desired to be protected.

What is claimed is:
 1. A probe card assembly comprising: a plurality ofprobes attached to a surface of a substrate; and a stop structureattached to said surface of said substrate.
 2. The probe card assemblyof claim 1, wherein said stop structure comprises a sensor.
 3. The probecard assembly of claim 2, wherein said probes are disposed in an array,wherein said apparatus further comprises a plurality of said stopstructures.
 4. The probe card assembly of claim 3, wherein at least twoof said plurality of stop structures are disposed on opposite sides ofsaid array.
 5. The probe card assembly of claim 1 further comprisingsensing means for determining contact between a device to be tested andsaid stop structure.
 6. The probe card assembly of claim 1 furthercomprising sensing means for determining a level of a force against oneof said probes.
 7. The probe card assembly of claim 1, wherein: eachsaid probe comprises a contact tip disposed a first distance from saidsurface of said substrate; and said stop structure comprises a stopfeature disposed a second distance from said surface of said substrate.8. The probe card assembly of claim 7, wherein said second distance isless than said first distance.
 9. The probe card assembly of claim 1,wherein said probes are compressible and said stop structure limitscompression of said probes.
 10. The probe card assembly of claim 9,wherein said probes are resilient.
 11. The probe card assembly of claim1, wherein said stop structure is compressible.
 12. The probe cardassembly of claim 11, wherein said stop structure is resilient.
 13. Theprobe card assembly of claim 1 further comprising a second substratecomprising a flexible material and configured to flex in response to aforce applied to said stop structure.
 14. The probe card assembly ofclaim 1 further comprising a plurality of said stop structures.
 15. Amethod of making a probe card assembly, said method comprising: forminga plurality of probes on a surface of a substrate; and forming a stopstructure on said surface of said substrate.
 16. The method of claim 15,wherein said forming a plurality of probes and said forming a stopstructure comprise: lithographically forming a plurality of tipstructures and a stop plate on a sacrificial substrate; and transferringsaid tip structures to a plurality of probe bodies attached to saidsurface of said substrate; and transferring said stop plate to a stopsupport attached to said surface of said substrate.
 17. The method ofclaim 16, wherein: said transferring said tip structures to a pluralityof probe bodies attached to said surface of said substrate, and saidtransferring said stop plate to a stop support attached to said surfaceof said substrate comprise: attaching said tip structures to said probebodes; attaching said stop plate to said stop support; and and releasingsaid tip structures and said stop plate from said sacrificial substrate.18. The method of claim 16, wherein said lithographically forming aplurality of tip structures and a stop plate on a sacrificial substratecomprises: patterning a plurality of masking layers; and depositingmaterial within said patterned masking layers to form said tipstructures and said stop plate.
 19. The method of claim 18, wherein saidpatterned masking layers define shapes of said tip structures and saidstop plate.
 20. The method of claim 18, wherein said patterned maskinglayers define relative locations of said tip structures and said stopplate.
 21. The method of claim 20, wherein contact portions of said tipstructures are located in a first plane and a contact portion of saidcontact structure is located in a second plane, and said first plane isa predetermined distance from said second plane.
 22. The method of claim15, wherein said probes are compressible and said stop structure limitscompression of said probes.
 23. The method of claim 22, wherein saidprobes are resilient.
 25. The method of claim 15 further comprisingsecuring said substrate to a second substrate, wherein said secondsubstrate is flexible.
 26. The method of claim 15 further comprisingconfiguring said stop structure to sense contact with another device.27. The method of claim 15, wherein said forming a stop structure onsaid surface of said substrate comprises forming a plurality of saidstop structures on said surface of said substrate.
 28. The method ofclaim 27, wherein said forming a plurality of probes on a surface ofsaid substrate comprises forming said plurality of probes in an array;said method further comprising configuring at least two of saidplurality of stop structures to sense contact with another device. 29.The method of claim 28 further comprising forming said two of said stopstructures on opposite sides of said array.
 30. A method of controllingrelative movement between an electronic device to be tested and a probecard assembly, said method comprising: effecting relative movement ofsaid device and said probe card assembly; detecting a desired amount ofover travel between said wafer and said probe card assembly; and upondetecting said desired amount of over travel, stopping said relativemovement of said device and said probe card assembly.
 31. The method ofclaim 30, wherein said detecting said desired amount of over travelcomprises detecting contact between a stop structure on said probe cardassembly and said device.
 32. The method of claim 30, wherein saiddetecting said desired amount of over travel comprises detecting contactbetween a plurality of stop structures on said probe card assembly andsaid device.
 33. A media for storing machine-executable instructions forcausing a controller to perform a method of controlling relativemovement of a device to be tested and a probe card assembly, said methodcomprising: generating a control signal to effect relative movement ofsaid device and said probe card assembly; receiving an input signalindicating completion of a desired amount of over travel between saidwafer and said probe card assembly; and in response to said inputsignal, generating a control signal to stop said relative movement ofsaid device and said probe card assembly.
 34. A method of controllingrelative movement between an electronic device to be tested and a probecard assembly, said method comprising: effecting relative movement ofsaid device and said probe card assembly; determining a force of saiddevice against said probe card assembly; and stopping said movement whensaid force exceeds a maximum force.
 35. The method of claim 34 furthercomprising. adjusting a speed of said movement in accordance with saidforce.
 36. The method of claim 35, wherein said adjusting a speed ofsaid movement in accordance with said force comprises decreasing saidspeed as said force increases.
 37. A media for storingmachine-executable instructions for causing a controller to perform amethod of controlling relative movement of a device to be tested and aprobe card assembly, said method comprising: generating a control signalto effect relative movement of said device and said probe card assembly;receiving an input signal corresponding to a force of said deviceagainst said probe card assembly; and generating a control signal tostop said movement when said force exceeds a maximum force.
 38. Themedia of 37, wherein said method further comprises generating a controlsignal to adjust a speed of said movement in accordance with said force